Which of the following statements about refrigerant blends is true?

• A. They have a single boiling temperature
• B. They maintain a constant composition during phase changes
• C. They can exhibit glide due to varying boiling temperatures
• D. They are generally less efficient than single-component refrigerants

Answer: (C)

Refrigerant blends are mixtures of two or more refrigerants, and they can exhibit a phenomenon known as "temperature glide." This occurs because each component in the blend has its own distinct boiling point. When a refrigerant blend changes phase—such as when it evaporates or condenses—the different components of the blend do not all change at the same temperature. Instead, there is a range of temperatures over which phase changes occur, leading to a gradual change in temperature rather than a sharp transition. This property of refrigerant blends allows them to utilize varying boiling points effectively in a refrigeration cycle, providing some advantages in specific applications.

In contrast, single-component refrigerants have a single boiling temperature and exhibit a more straightforward phase change behavior. The idea of maintaining a constant composition during phase changes applies to pure substances rather than blends since the components of a blend can separate under certain conditions, affecting efficiency. Moreover, while there may be instances where blends are less efficient, this is not a definitive characteristic of all blends compared to single-component refrigerants. The main point of distinction for blends is indeed their ability to exhibit glide due to varying boiling temperatures.